CVE-2021-47036

Summary

CVE-2021-47036 is a vulnerability affecting the Linux kernel that could lead to protocol corruption when NETIF_F_GRO_FRAGLIST or NETIF_F_GRO_UDP_FWD are enabled and UDP tunnels are available in the system. The issue occurs when udp_gro_receive() performs L4 aggregation at the outer UDP tunnel level, causing inner protocol headers to be ignored and leading to unexpected behavior. To mitigate this issue, the patch skips the SKB_GSO_UDP_L4 and SKB_GSO_FRAGLIST code path for packets that could land in a UDP tunnel and instead lets udp_gro_receive() handle GRO via udp_sk(sk)->gro_receive. However, the check implemented in the patch is broader than necessary, potentially disabling GRO for some packets unnecessarily. The commit message could be clarified in the update to version 2.

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